strtok() has at least these problems:
It merges adjacent delimiters. If you use a comma as your delimiter, then
"a,,b,c"is three tokens, not four. This is often the wrong thing to do. In fact, it is only the right thing to do, in my experience, when the delimiter set is limited to white space.
The identity of the delimiter is lost, because it is changed to a null terminator.
It modifies the string that it tokenizes. This is bad because it forces you to make a copy of the string if you want to use it later. It also means that you can't tokenize a string literal with it; this is not necessarily something you'd want to do all the time but it is surprising.
It can only be used once at a time. If a sequence of
strtok()calls is ongoing and another one is started, the state of the first one is lost. This isn't a problem for small programs but it is easy to lose track of such things in hierarchies of nested functions in large programs. In other words, strtok() breaks encapsulation.